The AAA ATPase p97 (also known as valosin-containing protein (VCP), Cdc48 in yeast and plants, CDC-48 in worms and Ter94 in flies), is a hexameric member of the \ AAA family (ATPases associated with diverse cellular activities). Zhang et al., “Structure of the AAA ATPase p97,” Molecular Cell, 6(6): 1473-84 (2000).
Recent studies have uncovered cellular functions for p97 in autophagy, endosomal sorting and regulating protein degradation at the outer mitochondrial membrane, and elucidated a role for p97 in key chromatin-associated processes. These findings extend the functional relevance of p97 to lysosomal degradation and reveal a dual role in protecting cells from protein stress and ensuring genome stability during proliferation. Meyer et al., “Emerging functions of the VCP/p97 AAA-ATPase in the ubiquitin system,” Nature Cell Biology, 14: 117-123 (2012).
p97 also functions as an interaction hub, and different sets of at least 30 cofactors have been shown to be responsible for modulating p97-mediated processes. Meyer et al., “The VCP/p97 system at a glance: connecting cellular function to disease pathogenesis,” J. of Cell Sci., 127: 1-7 (2014).
p97-Associated Disease and Possible Mechanisms: p97 is a potential therapeutic target for cancer and neurodegenerative diseases. Given the crucial role of p97 in maintaining cellular proteostasis, it is not surprising that autosomal dominant mutations in p97, the gene encoding p97, lead to a rare multisystem degenerative disorder previously termed IBMPFD/ALS. The acronym IBMPFD/ALS refers to the four main phenotypes that can affect patients carrying disease-associated mutations of p97 (i.e., inclusion body myopathy (IBM), Paget's disease of the bone (PDB), frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS)). However, a patient with a pathogenic p97 mutation can have any mixture of phenotypes, including all four phenotypes or just one phenotype in isolation. In addition, a member of the same family can have any combination of phenotypes. Id.
Some carriers of p97 mutation also manifest additional symptoms, including Parkinsonism, ataxia, cataracts, dilated cardiomyopathy, hepatic fibrosis, and hearing loss. The term multisystem proteinopathy’ has been proposed as the nomenclature for an emerging family of genetic disorders that are unified by this characteristic variation in the penetrance of muscle, bone and CNS degenerative phenotypes along with the accumulation of ubiquitin and TDP-43-positive inclusions.
p97 and Cancer: p97 figures prominently in protein quality control as well as serving a variety of other cellular functions associated with cancer. As found for other chaperones, various forms of cancer, including breast, lung, pancreatic, and colorectal cancer, upregulate p97 as a response to accelerated growth and deteriorating protein quality control. See Brandvold et al, “The chemical biology of molecular chaperones—implications for modulation of proteostasis,” J. Mol. Biol., 427(18): 2931-2947 (2015); Manos-Turvey et al., “The effect of structure and mechanism of the Hsp70 chaperone on the ability to identify chemical modulators and therapeutics,” Top. Med. Chem., 16:1-49 (2015); Deshaies, R. J., “Proteotoxic crisis, the ubiquitin-proteasome system, and cancer therapy,” BMC Biology, 12: 94/1-94/14 (2014); and Haines, D. S., “P97-containing complexes in proliferation control and cancer: Emerging culprits or guilt by association?” Genes Cancer, 1:753-763 (2010). This property might render cancer cells more sensitive to p97 inhibitors than normal cells. In particular, combinations with proteasome or heat shock protein inhibitors could further widen the therapeutic window, but the test of this hypothesis awaits the development of clinically efficacious p97 antagonists.
Several small molecule inhibitors of p97 have been identified. See Davies et al., “Improved structures of full-length p97, an AAA ATPase: Implications for mechanisms of nucleotide-dependent conformational change,” Structure, 16:715-726 (2008). This includes several amino-heterocycles, such as the diaminoquinazolines 1, 2, and 3, aminothiazole 4, and the irreversible inhibitor chloroacetamide 5 (FIG. 1). See Chou et al., “Reversible inhibitor of p9′7, DBeQ, impairs both ubiquitin-dependent and autophagic protein clearance pathways,” Proc. Natl. Acad. Sci. USA, 108:4834-4839 (2011); Fang et al., “Evaluating p97 inhibitor analogues for their domain selectivity and potency against the p97-p47 complex,” ChemMedChem, 10, 52-56 (2015); Zhou et al., “Preparation of fused pyrimidines as inhibitors of p97 complex,” WO 2014/015291; Chem. Abstr., 160:248915 (2014); Bursavich et al., “2-Anilino-4-aryl-1,3-thiazole inhibitors of valosin-containing protein (VCP or p9′7),” Bioorg. Med. Chem. Lett., 20:1677-1679 (2010); Magnaghi et al., “Covalent and allosteric inhibitors of the ATPase VCP/p97 induce cancer cell death,” Nat. Chem. Biol., 9:548-556 (2013). 1,2,4-Triazole 6, sulfonate 7, and imidazolinone 8 were identified by high throughput screening campaigns, whereas the discovery of the anticancer agent 9 (sorafenib) and the natural products 10 (withaferin A) and 11 (rheoemodin) as p97 inhibitors was based on specific mechanism of action and targeted lead identification studies. See Polucci et al., “Alkylsulfanyl-1,2,4-triazoles, a new class of allosteric valosine containing protein inhibitors. Synthesis and structure-activity relationships,” J. Med. Chem., 56: 437-450 (2013); Kakizuka et al., “Preparation of 2-(arylazo or heteroarylazo)-4-aminonaphthalene-1-sulfonic acid derivatives as regulators of vasolin-containing protein (VCP),” WO 2012/014994; Wang et al., “Inhibition of p97-dependent protein degradation by eeyarestatin I,” J. Biol. Chem., 283: 7445-7454 (2008); Yi et al., “Sorafenib-mediated targeting of the AAA+ATPase p97/VCP leads to disruption of the secretory pathway, endoplasmic reticulum stress, and hepatocellular cancer cell death,” Mol. Cancer Ther., 11:2610-2620 (2012); Tao et al., “Withaferin A analogs that target the AAA+chaperone p97,” ACS Chem. Biol., 10(8): 1916-1924 (2015); Kang et al., “Functional chromatography reveals three natural products that target the same protein with distinct mechanisms of action,” ChemBioChem, 15, 2125-2131 (2014).
There remains a need in the art for inhibitors of p97, useful in treating cancer and neurodegenerative disorders caused by proteostatic malfunction. The present invention satisfies these needs.